1. Field of the Invention
The present invention relates to an image reading method and apparatus, and particularly to an image reading method and apparatus, in which light is illuminated onto a developed photosensitive material, and based on the light transmitted through the photosensitive material, images recorded on the photosensitive material are read.
2. Description of the Related Art
There has been proposed in recent years a photographic processing method in which film images recorded on a developed photosensitive material such as a photographic film (hereinafter referred to merely as photographic film) are read in a state of being separated into component colors of R, G, and B and image data obtained by the reading is subjected to image processing including various corrections, and thereafter, an image is recorded on a recording material or is displayed on a display.
In an image reading apparatus used when film images are read using this type of photographic processing method, generally, light is irradiated on a film image and light transmitted through the film image is used to form an image, and further, a film image of a photographic film to be read is read, as image data comprised of a plurality of pixels, by an image sensor provided at an image-formation position, for example, a line CCD or an area CCD. The photographic film includes a negative film on which a negative image is recorded, and a positive film (a reversal film) on which a positive image is recorded.
In the image reading apparatus as described above, in order to correct variation of photoelectric transfer characteristics between every pixel of the image sensor, and further, in order to correct illumination unevenness, generally, light correction (shading correction) which allows correction of image data read by the image sensor for each pixel is performed.
In a conventional light correction method, based on image data obtained by reading a film image for adjustment whose entire image plane has a constant density, light correction data for each of pixels forming the image sensor is previously obtained and stored, and image data for each of pixels of a photographic film to be read is corrected in accordance with the above-described light correction data.
However, in the above-described light correction method, there is a problem that prior to reading of images on a photographic film to be read, it is necessary to read a film image for adjustment, for which operation is very complicated.
In order to solve the above-described problem, in the art disclosed in Japanese Patent Application Laid-Open (JP-A) No. 5-7296, at the time of reading images of a photographic film to be read, light correction data is acquired based on image data of a non-image region between image frames.
Further, in the art disclosed in Japanese Patent Application Laid-Open (JP-A) No. 10-75354, there is disclosed a method for acquiring light correction data without using a photographic film.
In the method disclosed in JP-A No. 5-7296, the light correction data is acquired from a non-image region between image frames on a photographic film to be read. For this reason, there are problems: it is difficult to reliably acquire light correction data when a space between image frames is narrow, and when a photographic film to be read is a positive film, the light correction data cannot be acquired from a non-image region of the positive film.
On the other hand, the method disclosed in JP-A No. 10-75354 does not use a photographic film for the purpose of saving labor at the time of acquiring the light correction data. Here, there is a problem that the color balance of R, G, and B of an image sensor at the time of acquiring the light correction data is remarkably different from the color balance of R, G, and B at the time of reading a photographic film, thereby resulting in that, when the image sensor has leakage sensitivity, light correction cannot be properly performed.
The present invention has been devised to solve the above-described problems, and an object thereof is to provide an image reading apparatus and method, in which light correction data can reliably be obtained accurately and without requiring a complicated operation.
In order to achieve the above-described object, an image reading apparatus according to a first aspect of the present invention comprises: a light source which emits light for illuminating a photosensitive material; an image sensor which reads an image recorded on the photosensitive material in a state of being separated into a plurality of pixels, and outputs the read image as image data; and adjusting means for adjusting the color balance of illuminating light emitted from said light source so that respective outputs of channels of said image sensor become substantially uniform both at the time of generation of light correction data and at the time of operation for light correction.
In accordance with the image reading apparatus and the image reading method relating to the first aspect of the present invention, both at the time of generation of light correction data and at the time of operation for light correction, the color balance of illuminating light emitted from the light source, which emits light for illuminating the photosensitive material to be read, is adjusted by the adjusting means so that respective outputs of channels (of red (R), green (G), and blue (B), or of cyan (C), magenta (M), and yellow (Y)) of the image sensor, the image sensor reading an image recorded on the photosensitive material in a state of being separated into, a plurality of pixels and outputting the read image as image data, become substantially uniform.
As described above, according to the image reading apparatus and the image reading method relating to the first aspect of the present invention, both at the time of generation of light correction data and at the time of operation for light correction, the color balance of illuminating light emitted from the light source is adjusted so that respective outputs of the channels of the image sensor become substantially uniform. Accordingly, respective states of the color balance of light emitted from the light source both at the time of generation of light correction data and at the time of operation for light correction can be made substantially uniform, and a complicated operation required when using a film image for adjustment of a constant density to generate light correction data becomes unnecessary. Further, even when a space between adjacent image frames of the photosensitive material is narrow, the light correction data can reliably be generated.
An image reading apparatus according to a second aspect of the present invention comprises: a light source which emits light for illuminating a photosensitive material; an image sensor which reads an image recorded on the photosensitive material in a state of being separated into a plurality of pixels, and outputs the read image as image data; a filter section including a negative-film color balance filter suitable for a negative film and a positive-film color balance filter suitable for a positive film, and disposed between said light source and said image sensor; light correction data generating means which generates light correction data based on data obtained by reading the positive-film color balance filter by said image sensor in a state without photosensitive material; and correction means which effects light correction for image data of the photosensitive material to be read based on the light correction data.
An image reading method according to a third aspect of the present invention comprises the steps of: generating in advance light correction data based on data obtained when, in a filter section which is disposed between a light source that emits light for illuminating a photosensitive material in a state of being separated into a plurality of pixels and outputs the read image as image data and which includes a negative-film color balance filter suitable for a negative film and a positive-film color balance filter suitable for a positive film, the positive-film color balance filter suitable for a positive film, the positive-film color balance filter suitable for a positive film is read by the image sensor in a state without photosensitive material; and based on the light correction data, effecting light correction for image data of a photosensitive material to be read.
In accordance with the image reading apparatus relating to the second aspect of the present invention and the image reading method relating to the third aspect of the present invention, the light correction data is generated based on an arithmetic mean value of data of identical pixels when the positive-film color balance filter is read by the image sensor a plurality of times without photosensitive material.
Here, the principle of the present invention will be described.
The positive-film color balance filter in the present invention is structured so that respective outputs of channels of the image sensor become substantially uniform when it is used at the time of reading a film image of a positive film. Similarly, the negative-film color balance filter is also structured so that respective outputs of channels of the image sensor become substantially uniform when it is used at the time of reading a film image of a negative film. Namely, these color balance filters are each designed so that a value obtained by integrating, by wavelength, an overall spectral characteristic provided by multiplying a spectral transmission factor of a photographic film, spectral distribution of light from illumination including the color balance filters, and spectral sensitivity of the image sensor by the wavelength becomes substantially uniform in each channel. On the other hand, a developed negative film usually inclines toward orange, and therefore, the negative-film color balance filter is provided to incline toward cyan which is complementary to that inclining to orange.
Accordingly, in reading a film image of a positive film using the positive-film color balance filter, when light correction is performed using light correction data generated using the negative-film color balance filter, respective outputs of channels of the image sensor cannot be made substantially uniform. As a result, proper light correction cannot be effected. On the other hand, in reading a film image of a negative film using the negative-film color balance filter, when light correction is performed using light correction data generated using the positive-film color balance filter, respective outputs of channels of the image sensor can be maintained in a substantially uniform state. As a result, proper light correction can be effected. Incidentally, in reading a film image of a positive film using the positive-film color balance filter, when light correction is effected using the light correction data generated using the positive-film color balance filter, proper light correction is of course allowed.
Accordingly, in the present invention, light correction data is acquired using the positive-film color balance filter, and the light correction data is provided so as to be used for light correction of both a positive film and a negative film.
The characteristics of CCD cells of one line in the channel of red (R) in a color line CCD when the photosensitive material to be read is a negative film, a color line CCD is used as the image sensor, and the negative-film color balance filter is used at the time of reading images on the photosensitive material (that is, at the time of reading a photographic film) were examined.
FIGS. 10A to 10D are graphs which show various states when light correction data is acquired without using any color balance filter. FIGS. 11A to 11D are graphs which show various states when light correction data is acquired using a positive-film color balance filter. Note that these figures each show measurement results of pixels in seven places, having sensitivities that differ by 10%. FIGS. 10A and 11A each show spectral characteristics of the above-described pixels in seven places when the light correction data is acquired, and FIGS. 10B and 11B each show spectral characteristics of the above-described pixels in seven places when a photographic film is read. FIGS. 10C and 11C each show respective shading amounts of the above-described pixels in seven places at the time of acquiring the light correction data and at the time of reading the photographic film, and FIGS. 10D and 11D each show residuals of respective shading amounts of the above-described pixels in seven places at the time of acquiring the light correction data and at the time of reading the photographic film.
Here, the pixels in seven places, having different sensitivities that differ by 10%, are provided such that the thickness of a color separation filter mounted on a light incident side of a line CCD varies every 10%. Accordingly, the transverse axis in FIGS. 10C, 11C, 10D, and 11D indicates a ratio (%) of change in the thickness of the color separation filter (that is, pixels provided every 10% of a range in which the ratio of change in the thickness is from xe2x88x9230% to +30%. Further, the vertical axis in FIGS. 10A, 11A, 10B, and 11B indicates an overall spectral characteristic of the entire apparatus. This is a spectral characteristic provided by multiplying, by wavelength, a spectral transmission factor of the photographic film (which is not considered in FIGS. 10A and 11A, and is considered only in FIGS. 10B and 11B), spectral distribution of illuminating light of illumination including the color balance filters, and a spectral sensitivity of the image sensor. The shading amount (%) represented by the transverse axis in FIGS. 10C and 11C is indicated by a normalized value so that it becomes 0% when the ratio of change in the thickness of the color separation filter is 0%.
The spectral characteristic at the time of acquiring light correction data shown in FIG. 10A and the spectral characteristic at the time of reading a photographic film shown in FIG. 10B greatly differ from each other in the graphical form in a wavelength region of about 500 nm or more.
As shown in FIG. 10C, a discrepancy occurs in the respective shading amounts in the pixels of seven places at the time of acquiring light correction data and at the time of reading the photographic film. It can be seen from the graph shown in FIG. 10D that a remaining difference between the shading amounts at the time of acquiring light correction data and at the time of reading a photographic film is large in the pixels when the ratio of change in the thickness of the color separation filter is 0% or less.
Accordingly, it can be understood that even if light correction is performed at the time of reading the photographic film using light correction data acquired without using the color balance filter, accurate light correction cannot be achieved.
On the other hand, in a case in which the positive-film color balance filter is used at the time of acquiring the light correction data, the spectral characteristic at the time of acquiring light correction data, which is shown in FIG. 11A, and the spectral characteristic at the time of reading a photographic film, which is shown in FIG. 11B, each have the substantially same graphical form.
In this case, as shown in FIG. 11C, a dicrepancy in the shading amount in the pixels of seven places at the time of acquiring light correction data and at the time of reading the photographic film is minimal. It can be seen from the graph shown in FIG. 11D that a remaining difference between the shading amounts at the time of acquiring light correction data and at the time of reading the photographic film is about 0% in all pixels.
Accordingly, it can be proved that when light correction is performed at the time of reading the photographic film using light correction data acquired using the positive-film color balance filter, highly accurate light correction can be achieved.
As described above, according to the image reading apparatus relating to the second aspect of the present invention and also according to the image reading method relating to the fourth aspect of the present invention, the color balance filter suitable for a negative film and the color balance filter suitable for a positive film are provided, and based on the data acquired by reading the color balance filter suitable for a positive film, light correction data which allows accurate light correction both for a negative film and for a positive film is generated. Accordingly, a complicated operation required when using a film image for adjustment of a constant density to generate light correction data becomes unnecessary, and even if a space between adjacent image frames on the photosensitive material is narrow, light correction data can reliably be generated with accuracy.
An image reading apparatus according to a third aspect of the present invention is characterized in that, in the image reading apparatus relating to the second aspect of the present invention, (claim 3). Further, an image reading method according to a fifth aspect of the present invention is characterized in that, in the image reading method relating to the fourth aspect of the present invention, (claim 5).
As described above, according to the image reading apparatus relating to the third aspect of the present invention and also according to the image reading method relating to the fifth aspect of the present invention, the light correction data in the second and fourth aspects of the present invention is generated based on an arithmetic mean value of data of identical pixels when the positive-film color balance filter is read by the image sensor a plurality of times in a state without the photosensitive material. Accordingly, the light correction data can be made into highly accurate data that is not easily susceptible to noise or the like.